There is a class of medical devices that are insertable into the body with a purpose, wholly or in part, to deliver a therapeutic agent. The intention is either to deliver the therapeutic agent locally at the location of insertion in the body, or to have the therapeutic agent elute systemically. In one implementation of local delivery it may be desired to have rapid delivery of the therapeutic agent to the body tissue, as is the case with some therapeutic agent (drug) coated balloon catheters. In another implementation of local delivery it may be desired to have sustained delivery of the therapeutic agent to the body tissue over a period of weeks or months, as is the case in drug eluting stents.
A polymer or oligomer is often used in the formulation of a coating matrix to contain and control the transfer of the drug into the tissue. In the case of long-term drug release profiles, the polymer can be hydrophobic to prevent dissolution in the aqueous environment of the body, so that the drug releases over time from the matrix via Fickian diffusion. In the case of short term drug release profiles, the polymer may have a hydrophilic character in order to partially dissolve or swell rapidly in the body, so as to help transfer the drug to the tissue upon contact with body fluids in a short period of time on the order of seconds or minutes.
The coating matrix and drug are typically applied to the medical device with a spray application or dip coating process, followed by drying. The coated medical device is then packaged and subjected to a sterilization process to kill any micro organisms which may have been left during production or packaging.
Ethylene oxide (EtO) sterilization is commonly used to sterilize medical and pharmaceutical products that may not be able to withstand high temperatures of a typical autoclave sterilization. A conventional three phase EtO sterilization process is summarized as including a pre-conditioning stage, a sterilizing stage, and an aeration stage. The pre-conditioning stage provides temperature and humidity conditions to incentivize micro organisms to come out of hibernation. The sterilization stage exposes the medical device to EtO gas at a specified temperature and pressure in order to kill the micro organisms. The aeration stage removes the EtO gas and allows the EtO gas to be desorbed.